Molded three-dimensional insulator

ABSTRACT

This invention provides a molded three-dimensional insulator that is suitable for use in an end cone region of a pollution control device. The invention also provides a method of making the insulator. The insulator includes ceramic fibers that have a bulk shrinkage no greater than 10 weight percent. The ceramic fibers contain alumina and silica and are microcrystalline, crystalline, or a combination thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/441,664 filed Jan. 22, 2003 and U.S. Provisional PatentApplication No. 60/456,736 filed on Mar. 21, 2003.

FIELD OF THE INVENTION

A molded three-dimensional insulator and a method of making theinsulator are provided. More specifically, a molded three-dimensionalinsulator for use in an end cone region of a pollution control device isprovided.

BACKGROUND OF THE INVENTION

Pollution control devices are used on motorized vehicles to reduceatmospheric pollution. Two types of pollution control devices arecurrently in widespread use: catalytic converters and diesel particulatefilters or traps. Catalytic converters contain one or more catalysts,which are typically coated onto a substrate in the form of a monolithicstructure. The monolithic structures are usually ceramic, although metalmonoliths have been used. The catalyst(s) can oxidize carbon monoxide,oxidize various hydrocarbons, reduce the oxides of nitrogen, or acombination thereof in exhaust gases. Diesel particulate filters ortraps are typically in the form of wall flow filters having ahoneycombed monolithic structure made from permeable crystalline ceramicmaterials. Alternate cells of the honeycombed monolithic structure areplugged so that the exhaust gas enters one cell, flows through thepermeable wall into another cell, and then exits the structure.

In state-of-the-art constructions of these pollution control devices,the monolithic structure is enclosed within a end cone housing. Becausethe monolithic structure typically has a larger diameter than an exhaustpipe from a vehicle, the end cone housing typically includes atransition zone. This transition zone, referred to as the end coneregion, narrows from a diameter suitable for the monolithic structure toa diameter suitable for connection to an exhaust pipe. The end cone isusually conical in shape and can be provided on both the inlet andoutlet side of the pollution control device.

Pollution control devices are usually operated at a relatively hightemperature such as, for example, above about 500° C. Consequently,insulation is typically provided within the end cone housing. Insulationmaterial in the form of a mounting mat can be placed between themonolithic structure and the metal housing. Insulation can also beplaced in the end cone region of the end cone housing. The end coneregion typically has a double-wall construction that includes an outerend cone housing and an inner end cone housing. Insulation material canbe placed between the inner and outer end cone housings.

SUMMARY OF THE INVENTION

This invention provides a molded three-dimensional insulator. Morespecifically, the insulator is suitable for use in an end cone region ofa pollution control device. The invention also provides a method ofmaking the insulator.

One aspect provides an article that includes a molded three-dimensionalinsulator having dimensions suitable for use in an end cone region of apollution control device. The insulator includes ceramic fibers having abulk shrinkage no greater than 10 percent using a Thermal MechanicalAnalyzer test (i.e., a sample of the ceramic fibers, under a load ofabout 50 psi (345 kN/m²), is heated to 1000° C. and then cooled; thecaliper of the sample at 750° C. during the heating step is compared tothe caliper of the sample at 750° C. during the cooling step). Theinsulator is self-supporting, seamless, and has a compressibility valueno greater than 750 kN/m² when the mount density is about 0.4 g/ml. Thearticle can further include an end cone housing for a pollution controldevice attached to an inner surface of the insulator, an outer surfaceof the insulator, or a combination thereof.

A second aspect of the invention also provides an article that includesa molded three-dimensional insulator having dimensions suitable for usein an end cone region of a pollution control device. The insulatorincludes ceramic fibers that contain at least 20 weight percent aluminaand at least 30 weight percent silica based on the weight of the fibers.The ceramic fibers can be microcrystalline, crystalline, or acombination thereof. The insulator is self-supporting, seamless, and hasa compressibility value no greater than 750 kN/m² when the mount densityis about 0.4 g/ml. The article can further include an end cone housingfor a pollution control device attached to an inner surface of theinsulator, an outer surface of the insulator, or a combination thereof.

A third aspect of the invention provides a method of making an articlethat includes an insulator suitable for use in an end cone region of apollution control device. The method involves preparing an aqueousslurry, vacuum forming a molded three-dimensional preform from theaqueous slurry on a permeable forming die, and drying the preform toproduce the molded three-dimensional insulator. The aqueous slurry usedto prepare the preform includes ceramic fiber having a bulk shrinkage nogreater than 10 percent based on the Thermal Mechanical Analyzer test.The insulator is self-supporting and has a compressibility value nogreater than 750 kN/m² when the mount density is about 0.4 g/ml.

A fourth aspect of the invention provides a method of making an articlethat includes an insulator suitable for use in an end cone region of apollution control device. The method involves preparing an aqueousslurry, vacuum forming a molded three-dimensional preform from theaqueous slurry on a permeable forming die, and drying the preform toproduce the molded three-dimensional insulator. The aqueous slurry usedto prepare the preform includes ceramic fiber that contain at least 20weight percent alumina and at least 30 weight percent silica. Theceramic fibers can be microcrystalline, crystalline, or a combinationthereof. The insulator is self-supporting and has a compressibilityvalue no greater than 750 kN/m² when the mount density is about 0.4g/ml.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The Figures and the detailed description that follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a pollution control device havinga molded-three dimensional insulator between an inner end cone housingand outer end cone housing.

FIG. 2 shows a perspective view of one embodiment of a moldedthree-dimensional insulator suitable for use in the end cone region of apollution control device.

FIG. 3 shows a perspective view of another embodiment of a moldedthree-dimensional insulator suitable for use in the end cone region of apollution control device.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawing and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides an article having a molded three-dimensionalinsulator suitable for use in the end cone region of a pollution controldevice and a method of making the article. As used herein, the phrase“molded three-dimensional insulator” refers to an insulating articlethat is not formed from a flat sheet of insulation material. Rather, theinsulator is formed using a mold or die having a three-dimensionalshape. Unlike insulators formed from a sheet, the moldedthree-dimensional insulator does not have a seam or seams that can beopened to provide a flat insulation article.

FIG. 1 shows a typical pollution control device having an insulatorpositioned between an inner end cone housing and an outer end conehousing. The pollution control device 10 includes an end cone housing 12with a generally conical inlet 14 and outlet 16. The housing, which isalso referred to as a can or a casing, is usually made of metal such asstainless steel. Disposed within the housing 12 is a monolithicstructure 18 made of a ceramic or metallic material. The monolithicstructure can include a catalyst. An insulating material 22 surroundsthe monolithic structure 18.

The inlet 14 and outlet 16 regions of the metal housing include an innerend cone housing 28 and an outer end cone housing 26. Insulationmaterial 30 is positioned between the inner end cone housing 28 and theouter end cone housing 26. The molded three-dimensional insulator of thepresent invention can be used as insulation material 30.

End cone insulation prepared from flat sheets or mats is known. The flatsheets or mats of insulation material can be cut to the desired size andshape and then formed to fit within the end cone region. For example,the flat sheet can be cut and formed into a conical shape having seams.The need to cut the sheet or mat to the desired size and shape resultsin some wasting of the insulation material. A molded three-dimensionalinsulator could result in the generation of less waste. Further, it canbe difficult or impossible to cut a flat sheet to fit an end cone havinga complex shape.

Molded three-dimensional insulators containing ceramic fibers are known.However, some of the insulators have been too stiff and difficult toposition between the inner and outer end cone housing of a pollutioncontrol device. Some of the insulators have been of a non-uniformthickness. Insulation materials having a non-uniform thickness can alsobe difficult to position in the end cone region of a pollution controldevice.

One aspect provides an article that includes a molded three-dimensionalinsulator having dimensions suitable for use in an end cone region of apollution control device. The insulator includes ceramic fibers having abulk shrinkage no greater than 10 percent using the Thermal MechanicalAnalyzer test. The insulator is self-supporting, seamless, and has acompressibility value no greater than 750 kN/m² when the mount densityis 0.4 g/ml. The article can further include an end cone housing for apollution control device attached to an inner surface of the insulator,an outer surface of the insulator, or a combination thereof.

FIG. 2 shows one embodiment of a molded three-dimensional insulator 50having an inner surface 52 and an outer surface 54. The inner surface 52of the insulator 50 can be adjacent to an inner end cone housing of apollution control device. The outer surface 54 of the insulator 50 canbe adjacent to an outer end cone housing of the pollution controldevice. Other shapes can be used to provided a generally conical shapefor placement of the insulator in the end cone region of a pollutioncontrol device. One such shape is shown in FIG. 3.

Suitable ceramic fibers are those having a bulk shrinkage no greaterthan 10 percent using the Thermal Mechanical Analyzer (TMA) test. In theTVA test, a sample under a load (e.g., 50 psi or 345 N/m²) is heated to1000° C. and then cooled. The caliper of the sample can be measuredduring both the heating and cooling cycles at 750° C. to calculatepercent shrinkage. The percent shrinkage is equal to the difference inthe caliper at 750° C. during the heating and cooling step multiplied by100 and divided by the caliper at 750° C. during the heating step. TheTMA test can be used to characterize the ceramic fibers or an insulatorprepared from ceramic fibers. Most or all of the organic materials thatmay be present in an insulator are removed by time the temperature ofthe Thermal Mechanical Analyzer reaches 750° C.

In some embodiments, the ceramic fibers have a bulk shrinkage no greaterthan 10 percent, no greater than 8 percent, no greater than 6 percent,no greater than 4 percent, no greater than 3 percent, no greater than 2percent, or no greater than 1 percent. The ceramic fibers typicallyshrink at least 0.5 percent. In some embodiments, the ceramic fibershave a bulk shrinkage in the range of 0.5 to 2 percent, of 0.5 to 3percent, of 0.5 to 5 percent, or of 0.5 to 6 percent using the TMA test.

Examples of commercially available ceramic fibers having a bulkshrinkage no greater than 10 percent as supplied (i.e., the fibers canbe used as supplied without a heat treatment) include, but are notlimited to, fibers that are crystalline and that contain both Al₂O₃(i.e., alumina) and SiO₂ (i.e., silica). The weight ratio of Al₂O₃ toSiO₂ to (Al₂O₃: SiO₂) can be greater than or equal to 60:40, 65:35,70:30, 72:28, 75:25, 80:20, 90:10, 95:5, 96:4, 97:3, or 98:2. In somespecific examples, the ceramic fibers contain 60 to 98 weight percentAl₂O₃ and 2 to 40 weight percent SiO₂ based on the weight of the fibers.In other specific examples, the ceramic fibers contain 70 to 98 weightpercent Al₂O₃ and 2 to 30 weight percent SiO₂ based on the weight of thefibers. Traces of other oxides can be present. As used herein, the term“trace” refers to an amount no greater than 2 weight percent, no greaterthan 1 weight percent, or no greater than 0.5 weight percent.

Suitable ceramic fibers that are usable without any heat treatmentinclude, but are not limited, those commercially available fromMitsubishi Chemical (Tokyo, Japan) under the trade designation “MAFTEC”(e.g., MLS1, MLS2, and MLS3) with 28 weight percent SiO₂ and 72 weightpercent Al₂O₃ based on the weight of the fibers; from Saffil Limited(Widness Cheshire, U.K.) under the trade designation “SAFFIL” (e.g., SF,LA Bulk, HA Bulk, HX Bulk) with 3 to 5 weight percent SiO₂ and 95 toabout 97 weight percent Al₂O₃ based on the weight of the fibers; andfrom Unifrax (Tonawonda, N.Y.) under the trade designation “UNIFFIBERFRAX FIBERMAX” with 27 weight percent SiO₂ and 72 weight percentAl₂O₃ based on the weight of the fibers.

In some embodiments, commercially available ceramic fibers can be heattreated to provide ceramic fibers that have a bulk shrinkage less 10percent. Such fibers typically include both Al₂O₃ and SiO₂. The weightratio of Al₂O₃ to SiO₂ to (Al₂O₃: SiO₂) is greater than or equal to20:80, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, or 70:30. Theceramic fibers typically include at least 30 weight percent SiO₂ and atleast 20 weight percent Al₂0₃. For example, suitable ceramic fibers cancontain silica in an amount of 30 to 80 weight percent and alumina in anamount of 20 to 70 weight percent weight percent based on the weight ofthe fibers. In some specific examples, the ceramic fibers can containsilica in an amount of 40 to 60 weight percent and alumna in an amountof 40 to 60 weight percent based on the weight of the fibers. In otherspecific examples, the ceramic fibers can contain silica in an amount of45 to 55 weight percent and alumina in an amount of 45 to 55 weightpercent based on the weight of the fibers. Traces of other oxides can bepresent.

Exemplary ceramic fibers that are suitable after heat treatment include,but are not limited to, ceramic fibers commercially available fromThermal Ceramic (Augusta, Ga.) under the trade designation “KAOWOOL HABULK” with 50 weight percent SiO₂ and 50 weight percent Al₂O₃ based onthe weight of the fibers; from Thermal Ceramics under the tradedesignation “CERAFIBER” with 54 weight percent SiO₂ and 46 weightpercent Al₂O₃ based on the weight of the fiber; from Thermal Ceramicsunder the trade designation “KAOWOOL D73F” with 54 weight percent SiO₂and 46 weight percent Al₂O₃ based on the weight of the fiber; from Rath(Wilmington, Del.) under the trade designation “RATH 2300 RT” with 52weight percent SiO₂, 47 weight percent Al₂O₃, and no greater than 1weight percent Fe₂O₃, TiO₂, and others based on the weight of thefibers; from Rath under the trade designation “RATH ALUMINO-SILICATECHOPPED FIBER” with 54 weight percent SiO₂, 46 weight percent Al₂O₃, anda trace of others based on the weight of the fiber; from Vesuvius(Buffalo, N.Y.) under the trade designation “CER-WOOL RT” with 49 to 53weight percent SiO₂, 43 to 47 weight percent Al₂O₃, 0.7 to 1.2 weightpercent Fe₂O₃, 1.5 to 1.9 weight percent TiO₂, and no greater than 1weight percent others based on the weight of the fibers; from Vesuviusunder the trade designation “CER-WOOL LT” with 49 to 57 weight percentSiO₂, 38 to 47 weight percent Al₂O₃, 0.7 to 1.5 weight percent Fe₂O₃,1.6 to 1.9 weight percent TiO₂, and 0 to 0.5 weight percent others basedon the weight of the fibers; and from Vesuvius under the tradedesignation “CER-WOOL HP” with 50 to 54 weight percent SiO₂, 44 to 49weight percent Al₂O₃, 0 to 0.2 weight percent Fe₂O₃, 0 to 0.1 weightpercent TiO₂, and no greater than 0.5 weight percent others based on theweight of the fibers.

In other embodiments of ceramic fibers that are suitable after a heattreatment, the ceramic fibers contain SiO₂, Al₂O₃, and ZrO₂. The weightratio of Al₂O₃ to SiO₂ to (Al₂O₃:SiO₂) is greater than or equal to20:80, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, or 70:30. Thefibers contain at least 3 weight percent ZrO₂, at least 30 weightpercent SiO₂, and at least 20 weight percent Al₂O₃ based on the weightof the fiber. In some embodiments, the fibers contain up to 5 weightpercent, up to 7 weight percent, up to 10 weight percent, up to 12weight percent, up to 15 weight percent, up to 16 weight percent, up to20, or up to 25 weight percent ZrO₂ based on the weight of the fibers.The ceramic fibers can contain SiO₂ in an amount of 30 to 70, 40 to 65,45 to 60, 45 to 55, or 50 to 60 weight percent based on the weight ofthe fibers. The ceramic fibers can contain Al₂O₃ in an amount of 20 to60, 25 to 50, 25 to 45, 25 to 40, 25 to 35, 30 to 50, or 30 to 40 weightpercent based on the weight of the fibers. In some specific examples,the ceramic fibers contain 25 to 50 weight percent Al₂O₃, 40 to 60weight percent SiO₂, and 3 to 20 weight percent ZrO₂ based on the weightof the fibers. In other specific examples, the ceramic fibers contain 30to 40 weight percent Al₂O₃, 45 to 60 weight percent SiO₂, and 5 to 20weight percent ZrO₂ based on the weight of the fibers. Traces of otheroxides can be present.

Exemplary ceramic fibers that contain SiO₂, Al₂O₃, and ZrO₂ that aresuitable after heat treatment include those commercially available fromThermal Ceramic (Augusta, Ga.) under the trade designation “KAOWOOL ZR”and “CERACHEM” with 50 weight percent SiO₂, 35 weight percent Al₂O₃, and15 weight percent ZrO₂ based on the weight of the fiber; from Unifrax(Tonawonda, N.Y.) under the trade designation “UNIFRAX FIBERFRAXFIBERMAT” with 52 to 57 weight percent SiO₂, 29 to 47 weight percentAl₂O₃, and no greater than 18 weight percent ZrO₂ based on the weight ofthe fibers; from Unifrax under the trade designation “UNIFRAX FIBERFRAXDURABACK” with 50 to 54 weight percent SiO₂, 31 to 35 weight percentAl₂O₃, 5 weight percent ZrO₂, 1.3 weight percent Fe₂O₃, 1.7 weightpercent TiO₂, 0.5 weight percent MgO, and no greater than 7 weightpercent CaO based on the weight of the fibers; from Rath (Wilmington,Del.) under the trade designation “RATH 2600 HTz” with 48 weight percentSiO₂, 37 weight percent Al₂O₃, 15 weight percent ZrO₂, and no greaterthan 1 weight percent others based on the weight of the fibers; and fromVesuvius (Buffalo, N.Y.) under the trade designation “CER-WOOL HTZ” with44 to 51 weight percent SiO₂, 33 to 37 weight percent Al₂O₃, 13 to 19weight percent ZrO₂, 0.1 to 0.6 weight percent Fe₂O₃, 0.1 to 0.6 weightpercent TiO₂, and no greater than 1 weight percent others based on theweight of the fibers.

The ceramic fibers tend to devitrify (i.e., change, at least in part,from an amorphous state into a microcrystalline or crystalline state)during the heat treatment process. Usually, only a portion of theindividual ceramic fiber undergoes devitrification. That is, after heattreatment, the individual ceramic fibers contain amorphous material aswell as crystalline material, microcrystalline material, or acombination of crystalline and microcrystalline material.

Techniques such as transmission electron microscopy and x-raydiffraction can be used to characterize the amorphous, crystalline, ormicrocrystalline nature of ceramic fibers. As used herein, the term“amorphous” refers to ceramic fibers that are free of crystalline ormicrocrystalline regions. If the ceramic fibers are amorphous, nodiffraction peaks (i.e., no diffraction pattern) can be detected usingeither transmission electron microscopy or x-ray diffraction. If theceramic fiber contains regions having a small crystalline size (i.e.,microcrystalline), diffraction peaks (i.e., a diffraction pattern) canbe detected using transmission electron microscopy but not using x-raydiffraction. As used herein, the term “microcrystalline” refers toceramic fibers that have at least some regions with a crystallinecharacter and that have a crystal size detectable with transmissionelectron microscopy but not with x-ray diffraction. If the ceramicfibers contain regions having a larger crystalline size (i.e.,crystalline), a diffraction pattern can be obtained using x-raydiffraction. As used herein, the term “crystalline” refers to ceramicfibers that have at least some regions with a crystalline character andthat have a crystal size detectable with x-ray diffraction. The smallestcrystal sizes detectable using x-ray diffraction typically results in abroad diffraction pattern without well-defined peaks. Narrower peaksindicate a larger crystalline size. The width of the diffraction peakscan be used to determine the crystalline size.

In some applications, the ceramic fibers are heat treated at atemperature of at least 700° C. For example, the ceramic fibers can beheat treated at a temperature of at least 800° C., at a temperature ofat least 900° C., at a temperature of at least 1000° C., or at atemperature of at least 1100° C. Suitable heat treatment temperaturescan vary depending on the composition of the ceramic fibers and the timethe ceramic fibers are held at the heat treatment temperature. Suitableheat treatment methods and suitable heat-treated ceramic fibers arefurther described, for example, in International Patent Application WO99/46028 and U.S. Pat. No. 5,250,269, incorporated herein by reference.

There is a time-temperature relationship associated with the size ofcrystals or microcrystals that form during the heat treatment process.For example, the ceramic fibers can be heat treated at lowertemperatures for longer periods of time or at higher temperatures forshorter periods of time to produce a comparable state of crystallinityor microcrystallinity. The time at the heat treatment temperature can beup to 1 hour, up to 40 minutes, up to 30 minutes, up to 20 minutes, upto 10 minutes, up to 5 minute, up to 3 minutes, or up to 2 minutes. Forexample, the heat treatment temperature can be chosen to use arelatively short heat treatment time such as up to 10 minutes.

The temperature of the heat treatment can be chosen to be at least 20°C., at least 30° C., at least 40° C., at least 50° C., at lest 60° C.,at least 70° C., at least 80° C., at least 90° C., or at least 100° C.above the devitrification temperature (i.e., the temperature at whichthe ceramic fibers change from being an amorphous material to being amicrocrystalline or crystalline material). Suitable heat treatment timesand temperatures for the ceramic fibers can be determined usingtechniques such as, for example, Differential Thermal Analysis (DTA).The temperature for alumina-silica fibers is typically in the range of700° C. to 1200° C., in the range of 800° C. to 1200° C., in the rangeof 900° C. to 1200° C., or in the range of 950° C. to 1200° C.

A ceramic fiber that is completely amorphous usually shrinks more thanceramic fiber that contain regions that are microcrystalline,crystalline, or a combination thereof. When amorphous fibers are madeinto a molded three-dimensional article, the article tends to shrinkexcessively when heated to elevated temperatures such as thoseencountered in a pollution control device. When insulation materialcontaining amorphous fiber is used in the end cone region of thepollution control device, the insulation material that has shrunk uponheating tends to move around in the space between the inner and outerend cone housings. This movement can cause the insulation material tobreak apart and loose effectiveness as an insulator.

Ceramic fibers that are at least partially crystalline ormicrocrystalline can be fabricated into molded three-dimensionalinsulators that can be repeatedly heated to a temperature suitable foruse in a pollution control device and then cooled. Microcrystalline orcrystalline ceramic fibers tend to be resistant to further shrinkagethat could negatively impact the performance of the insulators.

For ceramic fibers that are subjected to heat treatment, the brittlenessof the fibers can be balanced with the low shrinkage characteristics.Crystalline or microcrystalline materials ceramic fibers tend to be morebrittle than amorphous ceramic fibers. Insulation material made fromcrystalline or microcrystalline ceramic fibers can more easily be brokenthan insulation prepared from amorphous fibers. On the other hand,crystalline or microcrystalline ceramic fibers tend to have a lowershrinkage than amorphous ceramic fibers.

The insulators of the invention have a compressibility value no greaterthan 750 kN/m², no greater than 700 kN/m², no greater than 650 kN/m², nogreater than 600 kN/m², no greater than 550 kN/m², no greater than 500kN/m², no greater than 450 kN/m², no greater than 400 kN/m², no greaterthan 300 kN/m², no greater than 200 kN/m², or no greater than 100 kN/m²when the mount density is 0.4 g/ml. The compressibility value is usuallyat least 50 kN/m² when the mount density is 0.4 g/ml; however,insulators having a lower compressibility value can be used if the mountdensity is greater than 0.4 g/ml. As used herein, the “mount density”refers to the density of the insulator within a fixed gap (e.g., theinsulator is typically under pressure). In some embodiments, thecompressibility value is at least 75 kN/m² or at least 100 kN/m² whenthe mount density is 0.4 g/mil. For example, the compressibility valuecan be in the range of 50 to 750 kN/m², 50 to 500 kN/m², 50 to 300kN/m², 75 to 400 kN/m², 75 to 300 kN/m², 100 to 400 kN/m², or 100 to 300kN/m². The insulators can be compressed without breaking ordisintegrating.

The insulator is usually flexible. As used herein, the term “flexible”refers to an insulator that can have its three-dimensional shapedistorted or bent to fit between the inner and outer housing in an endcone region of a pollution control device without cracking, breaking, orfalling apart. A flexible insulator usually can be compressed in thethickness direction.

A second aspect of the invention also provides a moldedthree-dimensional insulator having dimensions suitable for use in an endcone region of a pollution control device. The insulator includesceramic fibers that contain at least 20 weight percent alumina and atleast 30 weight percent silica based on the weight of the fibers. Theceramic fibers are microcrystalline, crystalline, or a combinationthereof. The insulator is self-supporting, seamless, and has acompressibility value no greater than 750 kN/m² when the mount densityis about 0.4 g/ml. Suitable ceramic fibers are described above. Thearticle can further include an end cone housing for a pollution controldevice attached to an inner surface of the insulator, an outer surfaceof the insulator, or a combination thereof.

The molded three-dimensional insulators are formed by initiallypreparing an aqueous slurry containing the ceramic fibers. Organicbinders can be included in the aqueous slurry composition in addition tothe ceramic fibers. Organic binders tend to improve the integrity,flexibility, and the handling characteristics of moldedthree-dimensional insulator. Insulation material that is more flexiblemay be easier to position between the inner and outer end cone housingsof a pollution control device.

Organic binders can be used in amounts up to 20 weight percent based onthe weight of the insulator. In some embodiments, the organic binder ispresent in amounts up to 10 weight percent, up to 5 weight percent, orup to 3 weight percent based on the weight of the insulator. The organicbinder is typically burned off the insulator when the insulator is usedat elevated temperatures such as those typically encountered in apollution control device.

Suitable organic binder materials can include aqueous polymer emulsions,solvent-based polymers, and solvent free polymers. The aqueous polymeremulsions can include organic binder polymers and elastomers in the formof a latex (e.g., natural rubber lattices, styrene-butadiene lattices,butadiene-acrylonitrile lattices, and lattices of acrylate andmethacrylate polymers or copolymers). The solvent-based polymeric bindermaterials can include a polymer such as an acrylic, a polyurethane, avinyl acetate, a cellulose, or a rubber based organic polymer. Thesolvent free polymers can include natural rubber, styrene-butadienerubber, and other elastomers.

In some embodiments, the organic binder material includes an aqueousacrylic emulsion. Acrylic emulsions advantageously tend to have goodaging properties and non-corrosive combustion products. Suitable acrylicemulsions can include, but are not limited to, commercially availableproducts such as those sold under the trade designation “RHOPLEX TR-934”(an aqueous acrylic emulsion having 44.5 weight percent solids) and“RHOPLEX HA-8” (an aqueous emulsion of acrylic copolymers having 45.5weight percent solids) from Rohm and Hass (Philadelphia, Pa.); under thetrade designation “NEOCRYL XA-2022” (an aqueous dispersion of an acrylicresins having 60.5 percent solids) available from ICI Resins US(Wilmington, Mass.); and under the trade designation “AIRFLEX 600BP DEV”(an aqueous emulsion of ethylene vinyl acrylate terpolymer having 55weight percent solids) from Air Products and Chemical, Inc.(Philadelphia, Pa.).

Organic binders can also include a plasticizer, a tackifier, or acombination thereof. Plasticizers tend to soften a polymer matrix andcan enhance the flexibility and moldability of the insulator. Forexample, the organic binder can include a plasticizer such as isodecyldiphenyl diphosphate commercially available under the trade designation“SANTICIZER 148” from Monsanto (St. Louis, Mo.). Tackifiers ortackifying resins can aid in holding the insulation material together.An example of a suitable tackifier is commercially available from EkaNobel, Inc. (Toronto, Canada) under the trade designation “SNOWTACK810A”.

The aqueous slurry can include an inorganic colloidal material. Theinorganic colloidal material can act as an inorganic binder, as acoagulant to facilitate removal of the ceramic fibers from the aqueousslurry to form a molded three-dimensional preform, as a filler material,or a combination thereof. The inorganic colloid is usually a clay or ametal hydroxide.

In some applications, the inorganic colloidal material is formed in thepresence of the ceramic fibers. The inorganic colloid material can beformed by adding one or more water-soluble precursors to the aqueousslurry. The precursor can react to form, for example, a metal hydroxidein the aqueous slurry. Forming the inorganic colloidal material in theaqueous slurry tends to minimize agglomeration of the inorganic colloidand enhance uniformity of the inorganic colloid distribution throughoutthe slurry and the resulting preform. The pH of the slurry should besufficiently high to form the metal hydroxide. The size of the colloidalparticles can be altered, for example, by variation of the pH, reactiontime and temperature, precursor concentration, and the relative ratio ofthe precursors. The pH of the slurry is typically at least about 3.Suitable inorganic colloidal materials can include a metal hydroxidesuch as, for example, aluminum hydroxide, silicon hydroxide, titaniumhydroxide, yttrium hydroxide, or a combination thereof.

An example of an inorganic colloidal metal hydroxide is aluminumhydroxide formed by the reaction of an alkali metal aluminate and analuminum salt. More specifically, aluminum hydroxide can form, forexample, from the reaction of sodium aluminate with aluminum sulfate,aluminum phosphate, aluminum chloride, aluminum nitrate, or a mixturethereof. As another example, colloidal aluminum hydroxide can be formedfrom aluminum sulfate by adjustment of the pH of the slurry to at leastabout 3.

The inorganic colloidal material is usually present in an amount nogreater than 50 weight percent based on the weight of the ceramicfibers. In some embodiments, the inorganic colloidal material is presentin an amount no greater than 40, no greater than 30 weight percent, nogreater than 20 weight percent based on the weight of the ceramicfibers. For example, an aluminum hydroxide colloid can be formed bymixing 1 to 20 weight percent sodium aluminate and 1 to 20 weightpercent aluminum sulfate based on the weight of the ceramic fibers. Inmore specific examples, an aluminum hydroxide colloid can be formed bymixing 3 to 15 weight percent sodium aluminate with 3 to 15 weightpercent aluminum sulfate or 5 to 12 weight percent sodium aluminate with5 to 12 weight percent aluminum sulfate. In still other examples, thealuminum hydroxide colloid can be formed from aluminum sulfate. Forexample, the aluminum hydroxide colloid can be formed from 10 to 40weight percent aluminum sulfate or from 15 to 30 weight percent aluminumsulfate based on the dry weight of the ceramic fibers. The percent ofeach precursor (e.g., aluminum sulfate or sodium aluminate) is based onthe dry weight of the precursor.

The inorganic colloidal material can function as a binder to holdtogether the ceramic fibers. In some applications, an inorganic bindercan improve the temperature resiliency of the insulator. An organicbinder typically decomposes at elevated temperatures, such as thetemperatures encountered in a pollution control device. An insulatorthat lacks an inorganic binder can, under some circumstances, breakapart and loose effectiveness as an insulation material.

The inorganic colloidal material can be uniformly distributed in themolded three-dimensional insulator. As such, the insulator is morelikely to remain intact during fabrication and use of an articlecontaining the insulator such as in a pollution control device.

In some embodiments, the article includes the molded three-dimensionalinsulator and one or two end cone housings of a pollution controldevice. The end cone housing can be adjacent to the inner surface,adjacent to the outer surface, or adjacent to both the inner and outersurface of the insulator (i.e., the insulator can be positioned betweentwo end cone housings). The end cone housing, in some applications, isattached to the insulator. The end cone housing if often attached byfrictional forces.

A third aspect of the invention provides a method of making an articlethat includes a molded three-dimensional insulator suitable for use inan end cone region of a pollution control device. The method involvespreparing an aqueous slurry, vacuum forming a molded three-dimensionalpreform from the aqueous slurry on a permeable forming die, and dryingthe preform to produce the molded three-dimensional insulator. Theaqueous slurry used to prepare the preform includes ceramic fiber havinga bulk shrinkage no greater than 10 percent based on the ThermalMechanical Analyzer test. The insulator is self-supporting and has acompressibility value no greater than 750 kN/m² when the mount densityis 0.4 g/ml.

The aqueous slurry often contains up to 30 weight percent solids basedon the weight of the slurry. For example, the slurry can contain up to20 weight percent or up to 10 weight percent solids based on the weightof the slurry. The slurry often contains at least 1 percent solids basedon the weight of the slurry. For example, the slurry can contain atleast 2 weight percent or at least 3 weight percent solids. In someembodiments, the slurry can contain 1 to 10, 2 to 8, or 3 to 6 weightpercent solids. Higher solids can be advantageous because less waterneeds to be removed to prepare the preform. However, slurries withhigher percent solids tend to be more difficult to mix.

The water used in the slurry can be well water, surface water, or waterthat has been treated to remove impurities such as salts and organiccompounds. When well or surface water is used in the aqueous slurry,salts (e.g., calcium and magnesium salts) present in the water canfunction as an inorganic binder. In some embodiments, the water isdeionized water, distilled water, or a combination thereof.

Other additives can also be included in the aqueous slurry composition.Such additives can include defoamers, flocculants, surfactants, and thelike. Strength enhancing agents can also be included such as, forexample, organic fibers and glass fibers. Suitable organic fibersinclude rayon and cellulose fibers.

In some applications, the slurry is free of intumescent materials.Intumescent materials tend to become separated from the moldedthree-dimensional insulator. Once free from the insulator, theintumescent material can move and impact the insulator or monolith. Forexample, if used in the end cone region of a pollution control device,the intumescent material could continuously impact the insulator ormonolith when the vehicle containing the pollution control device ismoving. The insulator has an increased tendency to disintegrate undersuch circumstances. If the disintegration is severe, the article can nolonger function as an insulation material. The monolith could also beginto plug if large debris is released into the inlet.

The aqueous slurry is typically prepared by initially adding the ceramicfibers to water and by mixing well. In some embodiments, a low-shearmixer is used. Any suitable mixing methods can be used that does notexcessively break the ceramic fibers. Heat treated fibers tend to breakmore easily than their non-heat treated counterparts. Ceramic fibersthat are microcrystalline tend to break less readily than heat treatedceramic fibers having a larger crystalline size.

The ceramic fibers in aqueous slurry compositions usually have anaverage length no greater than 40 mm. In some embodiments, the averagelength is no greater than 30 mm, no greater than 25 mm, no greater than20 mm, no greater than 15 mm, or no greater than 10 mm. The averagelength is typically greater than 0.5 mm. In some embodiments, theaverage length is greater than 1 mm or greater than 2 mm. For example,the average fiber length can be 0.5 mm to 40 mm, 0.5 mm to 25 mm, or 1mm to 40 mm.

The average diameter of suitable ceramic fibers is often no greater than20 microns. In some embodiments, the average diameter is no greater than10 microns or no greater than 8 microns. The average diameter istypically greater than 0.5 micron, 1 microns, or 2 microns.

Although the components of the aqueous slurry can be added in any order,an organic binder is often added after an aqueous slurry of the ceramicfibers has been formed. An inorganic colloidal material or theprecursors for the inorganic colloidal material can be added after theorganic binder has been added to the aqueous slurry. Mixing is continuedduring the reaction that forms the inorganic colloidal material toensure that the colloidal material is uniformly mixed throughout theslurry.

Any suitable type of molding technique or mold known in the art can beused to prepare a preform. In some applications, the moldedthree-dimensional preform can be prepared using a vacuum formingtechnique. A permeable forming die is placed in the slurry. The solidsin the slurry can deposit on the surface of the forming die when avacuum is drawn. In some applications, the forming die can be removedfrom the slurry and coupled with a shape-retaining device having thesame shape as the forming die. The deposited ceramic fibers arepositioned between the forming die and the shape-retaining device. Theshape-retaining device and the forming die can be pressed together tofurther remove water and produce a preform having a relatively smoothsurface and a relatively uniform thickness. The shape-retaining deviceor the forming die can be the male molding part (i.e., if the formingdie is the male molding part, then the shape-retaining device is thefemale molding part or if the forming die is the female molding part,then the shape-retaining device is the male molding part).

The permeable forming die can include, for example, a screen. The screensize can be chosen so that the liquid components but not the ceramicfibers pass through the screen. For example, the screens can be in thesize range of 20 (about 850 microns) to 80 mesh (about 180 microns) orin the size range of 30 (about 600 microns) to 80 mesh. If the mesh sizeis too fine, the screen is easily plugged. If the mesh size is toolarge, the screen does not retain the ceramic fibers (i.e., a preformcannot be formed). Under normal operating conditions, some of the solidsfrom the slurry deposit on the screen when a vacuum is pulled.

The preform can be dried to form a molded three-dimensional insulator.If the preform is fairly firm, it can be dried without being supported.That is, after being formed on the forming die, the preform can beremoved from the die for further drying. In some embodiments, thepreform is dried while being supported by the forming die, theshape-retaining device, or a combination thereof. This additionalsupport helps prevent the preform from collapsing until it becomes drierand firmer. The preform can be dried using any method known in the art.For example, the preform can be dried in an oven or at room temperature.When dried in an oven, the temperature can be up to about 200° C. Insome applications, the drying temperature can be up to about 150° C. orup to about 125° C.

In some applications, the preform can be dried while in contact with theforming die. A stream of air or nitrogen can be blown though the formingdie as part of the drying process. The air or nitrogen that is blownthrough the forming die can be at room temperature or at an elevatedtemperature. Additional air or nitrogen can be passed over or impingethe outer surface of the preform opposite the surface in contact withthe forming die.

In some applications, the molding process can be similar to thosedisclosed in U.S. Pat. Nos. 5,078,822 and 6,596,120 B2, the disclosureof which is incorporated herein by reference. The three-dimensionalpreform can be prepared using a die assembly that includes amulti-component die and a shape-retaining device. The multi-componentdie is a permeable forming die and usually includes an internal skeletonand an outer shell. The internal skeleton had a vacuum system throughits interior to provide vacuum pull and vacuum distribution throughoutthe die. The outer shell of the forming die has a screen. For example,the screen can have a mesh size of 20 to 80 mesh. The multi-componentforming die is permeable. The die assembly can be positioned in theslurry such that the multi-component forming die is separated from theshape-retaining device.

A vacuum can be connected to the multi-component forming die and a layercontaining ceramic fibers can deposit on the forming die. The outerdimensions of the deposited layer (i.e., the outer dimensions of thepreform) can be at least equal to, if not slightly larger than, theinterior dimensions of an outer housing for the end cone region of apollution control device into which the resulting insulator will beplaced. While in a wet condition, the die-supported preform can beinserted into the shape-retaining device (e.g., the shape-retainingdevice can be a outer end cone housing of a pollution control device).The forming die can be removed where the preform is partially insertedinto the shape-retaining device or when the preform is in full contactwith the shape-retaining device. In some applications, the preformcontacts the shape-retaining device while still being supported by theforming die.

Alternatively, the multi-component forming die can have dimensions and ashape that prepares a preform that fits over a shape-retaining device(e.g., the shape-retaining device can be an inner end cone housing of apollution control device). While in a wet condition, the formingdie-supported preform can be inserted onto the shape-retaining device.The die can be removed where the preform is partially inserted onto theshape-retaining device or when the preform is in full contact with theshape-retaining device. In some applications, the preform contacts theshape-retaining device while still being supported by the forming die.

Pressure can be applied to the preform to increase the level of contactbetween the preform and the shape-retaining device. That is, the preformcan be pressure fitted into the shape-retaining device. The preform canbe transferred to the shape-retaining device by removing the vacuumapplied to the forming die, by applying air or nitrogen through thepermeable forming die, or by other methods known in the art andwithdrawing the forming die. After the forming die is removed, thecombination of preform and shape-retaining device can be placed in anoven to evaporate water from the preform.

When pressure is applied to the preform positioned between the formingdie and the shape-retaining device, the preform can be pressure fittedto the shape-retaining device. In some applications, the preform can bedried within the shape-retaining device to prepare an insulator that isattached to the shape-retaining device, for example, by friction. Forexample, an insulator attached to an inner or outer end cone housing ofa pollution control device can be prepared.

Pressure fitting the preform to a shape-retaining device can result inthe formation of insulators having a relatively smooth surface. That is,an insulator prepared by pressing the preform into a shape-retainingdevice is typically smoother than an insulator prepared using only aforming die. Further, the thickness uniformity of the preform and theresulting insulator can typically be improved by pressure fitting thepreform to the shape-retaining device.

Pressure fitting the preform into a shape-retaining device can alsoresult in the formation of an insulator with clean edges. That is, theapplication of pressure tends to shear the ceramic fibers at the edge ofthe preform and reduce the number of ceramic fibers extending beyond theedges of the shape-retaining device.

In some applications, additional inorganic binders can be applied to thesurface of the molded three-dimensional insulator to further stiffen theinsulator. For example, a solution of an additional inorganic binder canbe applied to the inner or outer surface of the three-dimensional shapebefore or after drying. Suitable additional inorganic binders include,for example, alumina sols, titania sols, zirconia sols, colloidal silicasuspensions, clays, refractory coatings such as silicon carbidesuspensions, or solutions of an aluminum or phosphate salts. Theadditional inorganic binder is usually added in an amount to provide aninsulator that is flexible and conformable. If too much additionalinorganic binder is used, the insulator can become too stiff (i.e., notflexible) and non-compressible (i.e., compression value greater than 750kN/m² at a mount density of about 0.4 g/ml). The additional inorganicbinder usually can be added to the surface of the preform in an amountup to 10 weight percent on a dry weight basis of the preform orinsulator. For example, the additional inorganic binder can be added tothe surface in an amount up to 5 weight percent, up to 3 weight percent,or up to 1 weight percent on a dry weight basis of the preform orinsulator.

In some other applications, additional organic binders or material canbe applied as a coating to the inner surface of the insulator, outersurface of the insulator, or a combination thereof. Application of sucha coating can improve the smoothness of the insulator, reduce thefriction of the insulator, improve the ease of positioning the insulatorbetween the inner and outer housing in the end cone region of apollution control device, or combinations thereof. The organic coatingcan include, for example, a polyolefin material or an acrylic material.

The thickness of the insulator can vary depending on the application.The thickness can be affected by variables such as the dwell time andvacuum level. A longer dwell time (i.e., the length of time the formingdie is in the slurry under vacuum conditions) typically results in theformation of a thicker preform and insulator. Likewise, a strongervacuum with the same dwell time typically results in the formation of athicker preform and insulator. When used as insulation in the end coneregion of a pollution control device, the thickness of the insulatortypically ranges from 1 mm to 25 mm. In some embodiments, the thicknessis uniform across the shape. Thickness uniformity can be affected by thesize of the ceramic fibers (i.e., smaller ceramic fibers tend to producea preform having a more uniform thickness). Insulators with a fairlyuniform thickness can be easier to position between the outer and innerhousing in an end cone region of a pollution control device.

The bulk density (i.e., density in the absence of pressure) of themolded three-dimensional insulator can vary depending on the processused to prepare the insulator. The bulk density is typically in therange of 0.1 to 0.4 g/ml. In some embodiments, the insulator has a bulkdensity of 0.15 to 0.3, 0.2 to 0.4, or 0.2 to 0.3 g/ml.

A fourth aspect of the invention provides a method of making an articlethat includes a molded three-dimensional insulator suitable for use inan end cone region of a pollution control device. The method involvespreparing an aqueous slurry, vacuum forming a molded three-dimensionalpreform from the aqueous slurry on a permeable forming die, and dryingthe preform to produce the molded three-dimensional insulator. Theaqueous slurry used to prepare the preform includes ceramic fiber thatcontain at least 20 weight percent alumina and at least 30 weightpercent silica. The ceramic fibers can be microcrystalline, crystalline,or a combination thereof. The insulator is self-supporting and has acompressibility value no greater than 750 kN/m² when the mount densityis 0.4 g/ml.

The methods of preparing a molded three-dimensional insulator can beused to prepare seamless articles or articles with a seam. In someembodiments, the articles are seamless. As used herein, the term“seamless” refers to a molded three-dimensional insulator that does nothave any separation or discontinuity of materials forming the insulatorsuch as by a cut or notch in the insulation material. That is, aseamless insulator is free of notches, cuts, or other separations formedthrough a portion of the insulator to relieve stress. FIGS. 2 and 3 areperspective views of seamless, molded three-dimensional insulators. Anylines shown on the surface of the article are meant for shading purposesto suggest a three-dimensional shape.

In other embodiments, insulators with seams can be prepared. As usedherein, the term “seam” refers to a separation of material such as by acut or notch in the insulation material. The seam can be used, forexample, to relieve stress or to enhance the conformability of theinsulator during the canning process (i.e., in some applications, a seamcan improve the ability to position the insulator between an outer andinner end cone housing of a pollution control device). A seam can extendthrough part of the thickness of the insulator or through the entirethickness of the insulator.

The foregoing describes the invention in terms of embodiments foreseenby the inventor for which an enabling description was available,notwithstanding that insubstantial modifications of the invention, notpresently foreseen, may nonetheless represent equivalents thereto.

EXAMPLES Test Methods

Bulk Shrinkage

The bulk shrinkage of a mass of ceramic fibers was determined by ThermalMechanical Analysis (TMA) using a Theta Dilatronic II Thermal Analyzer,Model MFE-715 (obtained from Theta Industries, Inc., Port Washington,N.Y.) having a chart recorder. A sample of fiber was cut using acircular die having a diameter of 11 mm and placed on a platen in thefurnace. A 7 mm diameter quartz rod (about 35.6 cm long) supporting a1350 gram weight was placed over the sample and the furnace was closed.This corresponds to a load of about 50 psi (345 kN/m²) applied to thesample. The sample with the applied weight was allowed to stabilize forabout 5 minutes prior to heating to 1000° C. at a rate of 15° C./min.After the oven reached 1000° C., the furnace was turned off and cooledto room temperature. The sample was cooled within the furnace. Thethickness of the sample, measured as the gap between the end of the rodand the platen, was plotted on a chart recorder during both the heatingand cooling cycles. The percent shrinkage was calculated from thethickness (T1) recorded at 750° C. during the heating cycle and thethickness (T2) recorded at 750° C. during the cooling cycle. The bulkshrinkage was calculated as% Bulk Shrinkage=[(T1−T2)/T1]×100.

The TMA test can be used for samples with or without organic bindermaterials. Organic materials will usually burn out at about 500° C.During the heating cycle, the thickness of the sample measured at 750°C. is essentially the thickness of the mass of fibers with inorganicbinders and particles, if present. As the sample is heated further, anyshrinkage of the fibers that occurs up to 1000° C. will be apparentduring the cooling cycle if the thickness measured at 750° C. is lessthan the thickness of the sample during the heating cycle.

Compressibility

The compressibility was a measure of the resistance to compression of aninsulation material within a fixed gap at room temperature (e.g., about20° C. to about 25° C.) and is expressed as a force per unit area, kN/m²(kiloNewtons/meter²). The test was conducted on a square sample of theinsulation material measuring about 3.8 cm by 3.8 cm on a compressiontester made by MTS Systems Corp (Research Triangle Park, N.C.). Thetester had a stationary lower platen and an upper platen attached to aload cell. The sample was placed on the lower platen, and the upperplaten was lowered at a rate of 30.48 cm/minute to a fixed gap that wasdetermined by the desired mount density. The insulation materialexhibited a peak force when the upper platen first reached the gap setfor the mount density as it compressed the sample. The platen was thenstopped and held at that point for 15 seconds during which time theinsulation material relaxed and the force it exerted was reduced. Asused herein, the term “compression value” refers to the compressionmeasured after holding for 15 seconds. The compression value isdependent on the mount density.

The mount density is the density of an insulating material within aconfined gap (i.e., the insulation material is under pressure) as istypically found between two nesting concentric cone housings in a doublewalled end cone of a pollution control device (i.e., the end cone regiontypically includes the insulator positioned between an inner end conehousing and an outer end cone housing). The end cone housing refers tothe housing in the end cone region of the pollution control device. Themount density of the insulator positioned between the two end conehousings is usually, but not always, uniform throughout the insulator.The mount density (in grams/ml) is calculated as the basis weight of theinsulation material in grams/cm² divided by the gap in cm. The basisweight is determined by cutting out a known area of the insulator andweighing it.

In the assembly of the pollution control device having a double walledend cone, the insulator can be placed against the inner surface of theouter end cone housing and the outer surface of the inner end conehousing can be positioned against the insulator. Alternatively, theinsulator can be placed on the outer surface of the inner end conehousing and the insulator can then be positioned against the innersurface of the outer end cone housing. The two end cone housings arepressed together, compressing the insulator between the inner and outerend cone housing. The inner and outer end cone housings are typicallywelded together on the smaller end of the cone. This further compressesthe insulator within the gap between the two end cone housings such thatthere is typically a maximum force per area exerted by the insulatoragainst the two housings when the end cone housings are first weldedtogether. Within a short time the insulator usually relaxes between theinner and outer housings and exerts a lower pressure against thehousings. The reduced pressure is sufficient to hold the insulator inplace during use.

RCFT (Real Condition Fixture Test)

The RCFT modeled the conditions found in the gap of a double walled endcone on a metal pollution control device during normal use, and measuredthe pressure exerted by the insulating material as if it were mountedbetween the inner and outer end end cone housing of the device under theconditions modeled. The insulating material was placed between two 50.8mm by 50.8 mm stainless steel platens and the platens are closed so thatthe insulating material was at a mount density of 0.4 g/ml. The platenswere controlled independently and were heated to different temperaturesto simulate the temperatures of the outer end cone housing, which isexposed to cooler ambient temperature air, and the inner end conehousing, which is exposed to hot exhaust gases, of the pollution controldevice during use. The platens were heated to a set point temperature asindicated in Table 4 below. The gap between the platens decreased andthen increased by a value calculated from the coefficients of thermalexpansion of the inner and outer end cone housings at their respectivetemperatures. The gap decreased very slightly as the temperatureincreased up to about 450° C. on a first platen (i.e., Platen 1) tosimulate the slightly higher expansion that the inner end cone housingundergoes from being closer to the hot exhaust gases. As thetemperatures continued to increase, the gap increased slightly as themetal on the second platen (i.e., Platen 2) expanded. The temperaturesof the platens, Platen 1 simulating the inner end cone housing andPlaten 2 simulating the outer end cone housing, are shown in Table 4below. The pressure force exerted by the mounting material was measuredusing a Sintech ID computer-controlled load frame with an Extensometerobtained from MTS Systems Corp., Research Triangle Park, N.C. A suitableinsulator usually can exert pressure within the gap throughout theheating and cooling cycles and particularly during the 15 minutes whenthe platens are held at 900° C. and 530° C. when the pressure is likelyto be the lowest.

Example 1

A slurry containing 95.5 weight percent water, 2.95 weight percentceramic fibers, 0.95 weight percent sodium aluminate, and 0.6 weightpercent active aluminum sulfate (added in the form of a 50% aluminumsulfate solution in water) was prepared in a 5 gallon, plastic lineddrum. Using an industrial grade low-shear mixer at low speed, theceramic fibers were slowly added to 15.4 liters (l) of well water in thedrum while increasing the stirring speed of the mixer to disperse theceramic fibers and to break apart large clumps of fibers. When all ofthe ceramic fiber had been added, the sodium aluminate was added andmixed for approximately 3 minutes. The aluminum sulfate solution wasthen added slowly, and the slurry was mixed another 5 minutes until theslurry appeared uniform.

The ceramic fibers used in the preparation of this example werealuminosilicate fibers commercially available under the tradedesignation “KAOWOOL HA-BULK” from Thermal Ceramics, Augusta, Ga. Theceramic fibers have a composition of about 50% alumina and 50% silica.The fibers were heat treated to have a bulk shrinkage of 4.5% asdetermined by the TMA test. A sufficient amount of heat treating wasobtained by heating the bulk fibers for about 3 minutes at 1060° C. Theheat treated fibers had an average diameter of about 3 microns and anaverage length less than about 10 mm. When analyzed using x-raydiffraction, a broad peak was obtained at a 2θ angle of about 22.5degrees using a copper K_(α) line as the radiation source. The fiberscontained crystalline regions but the crystalline size was not largeenough to result in a narrow diffraction peak. The same fibers without aheat treatment had a bulk shrinkage of about 47% and were amorphous.

A preform was formed by dipping the screen side of a forming dieattached to a vacuum system into the uniformly mixed slurry. The die hadan elliptical conical section formed by a 50-mesh screen, and thepreform had the shape of a truncated elliptical cone that was open onthe top and the bottom. The opening at the top of the cone was anellipse having approximate diameters of 10.5 cm by 3.8 cm, and theopening on the bottom of the cone was an ellipse having approximatediameters of 12.1 cm by 4.3 cm. The cone about was 7 cm high. The wallsof the preform had a thickness in the range of about 1.5-15 mm dependingon the process conditions chosen. The dipping time and vacuum levelcould be varied to change sample thickness and basis weight to suit theend use.

When the desired wall thickness was attained, the die, with the preformattached, was removed from the slurry and the preform was covered with aplastic bag. The plastic bag simulated a female portion of a two-partmold to hold the materials of the preform in place. Vacuuming continueda few more seconds until the preform was relatively firm and most of thewater was out. The vacuum was then turned off and the preform wascarefully removed from the die by blowing compressed air through the dieto release the preform.

The preform was self-supporting (i.e., when placed on a surface, thepreform substantially maintained its shape without collapsing ordeforming). The preform was dried in an oven at 150° C. for 40 minutesto form a conically shaped three dimensional insulator suitable forinsulating an end cone region of a pollution device. The resultinginsulator was freestanding (i.e., the insulator could support its ownweight when placed on a flat surface without collapsing). When theinsulator was lightly compressed by hand in the thickness direction andthen released, it was slightly resilient (i.e., the insulator'sthickness tends to spring back, although not necessarily to its originalthickness, as long as the compression force does not exceed the crushstrength of the fibers).

Example 2

A slurry was prepared by adding about 178 liters of well water to astainless steel mixing tank equipped with an in-line propeller mixeroperating at medium-high speed. Slowly, 5.7 kg of heat treated ceramicfibers (described in Example 1) were added while the speed of the mixerwas increased to the maximum level to maintain the dispersion and tobreak apart large clumps of fibers. Then 1.1 kg of latex (an aqueousemulsion of ethylene vinyl acrylate terpolymer having 55 weight percentsolids, sold under the trade designation “AIRFLEX 600BP” by AirProducts, Philadelphia, Pa.) was added and mixed for about 5 minutes.The latex addition was followed by addition of 1.9 kg of active aluminumsulfate in a 50% solids aqueous solution, addition of another 178 litersof well water, and then addition of 90.7 grams of a defoamer(commercially available from Henkel, Germany under the trade designation“FOAMASTER III”). The slurry was mixed for about 10 minutes untiluniform, and then pumped into a plastic lined 55 gallon (208 liter)drum. On a dry weight basis (i.e., without water), the composition was78 weight percent heat treated ceramic fibers, 8 weight percent latex,13 weight percent aluminum sulfate, and 1 weight percent defoaamer.

The slurry in the drum was mixed again with a mixer and purged with airto form a uniform dispersion. A conical preform was prepared from theslurry by submerging a multi-component forming die into the slurry anddepositing solids from the slurry on the die until the desiredthickness, weight, and density were achieved. Sufficient solids from theslurry were deposited on the die so that when the preform was dried toform an insulator, it had a target thickness of about 8.0-9.0 mm, atarget weight of about 30 grams, and a target density of about 0.20g/ml.

The multi-component forming die construction included an internalskeleton and an outer shell. The internal skeleton had a vacuum systemthrough its interior to provide vacuum pull and vacuum distributionthroughout the die. The outer shell of the forming die had an openscreen having 900 openings per 6.45 square centimeters. The outer shellhad a shape and size of the outer surface of the inner end cone housingof a double walled end cone of a pollution control device (i.e., theouter shell had a shape corresponded to the inner end cone housing ofthe end cone region of a pollution control device).

The preform, while still damp, was released from the forming die anddried overnight at room temperature to form an insulator. Alternatively,the preform could be dried in an oven or by using other known dryingprocedures.

The resulting insulator had the shape of a truncated cone with acircular opening at the top measuring about 5.5 cm in diameter and anelliptical opening on the bottom with diameters of 15 cm by 10 cm. Theinsulator was about 4.5 cm high and about 8.2 mm thick. The freestandinginsulator was pliable (i.e., the insulator could be bent and flexedgently without breaking apart or cracking; a pliable insulator isflexible) and resilient. The insulator had a bulk shrinkage of about4.5%. The compressibility of the insulator material was tested and thedata is shown in Table 1. The values are the average of 3 tests on eachsample.

TABLE 1 Compression Force at Various Mount Densities for Example 2 15Sec Basis Wt Mount Density Gap Peak Force Force (g/m²) (g/ml) (cm)(kN/m²) (kN/m²) Sample 1 1822 0.3 0.533 157 78 Sample 2 1822 0.4 0.455322 161 Sample 3 1822 0.5 0.363 596 293

Example 3

A preform is prepared from the slurry of Example 2 using a die assemblyto form the preform within the outer end cone housing of a double walledend cone on a pollution control device (i.e., the outer end cone housingof the pollution control device). The die assembly for this preformincludes a multi-component forming die and a shape-retaining device. Themulti-component forming die has an internal skeleton and outer shell.The shape-retaining device is the outer end cone housing for a pollutioncontrol device. The multi-component die is similar to that describedabove for Example 2 except that the outer shell of the multi-componentforming die is slightly smaller, in all dimensions, than the inner endcone housing that would be used in the end cone region of a pollutioncontrol device. This smaller forming die allows the formation of apreform with the same outer dimensions as the shape-retaining device butwith thicker walls than would be produced with a larger forming die. Theshape-retaining device is arranged relative to the multi-componentforming die such that the slurry can move easily into the space betweenthe shape-retaining device and the forming die when the assembly issubmerged into the slurry and a vacuum is pulled in the forming die.When the desired thickness and density for the preform are attained, thevacuum is stopped and the entire assembly is lifted out of the slurry.The preform is inserted into the shape-retaining device while beingsupported by the forming die. Then, air is blown out of the forming dieto release the preform from the die and to force the preform into theshape-retaining device. The preform can be pressure fitted to theshape-retaining device. Pressure fitting can be used to prepare aninsulator with clean edges. As the preform is pressed between theforming die and the shape retention device, the ceramic fibers can besheared at the edge. That is, there are no excess fibers around the endsor edges of the end cone insulator.

The preform can be dried while in the shape-retaining device or afterremoval from the shape-retaining device. The preform can be dried atroom temperature (about 20° C. to about 25° C.) overnight to form aninsulator having similar dimensions and appearance to the insulator ofExample 2 except that the wall dimensions are thicker. The end coneinsulator is freestanding, pliable, and resilient. The increasedthickness permits the insulator to be compressed when the pollutioncontrol device is assembled, and the insulator can retain somecompression to hold it in place during use.

Example 4

A slurry was prepared according to the procedure described in Example 2except that the composition was 356 liters of water, 5.7 kg of heattreated ceramic fiber, 1.07 kg of latex (“AIRFLEX 600BP” later), 1.2 kgof a 50% solids aqueous solution of active aluminum sulfate, and 90.7grams of defoamer (“FOAMASTER III” defoamer). On a dry weight basis(i.e. without water), the composition was 82 weight percent heat treatedfiber, 8 weight percent latex, 9 weight percent aluminum sulfate, and 1weight percent defoamer. A preform was prepared according to theprocedure described in Example 3 except that the multi-component formingdie had approximately the same dimensions as the outside surface of theinner end cone housing in the end cone region of a pollution controldevice. A shape-retaining device was used as described in Example 3. Thepreform was likewise air dried overnight to form an insulator.

The appearance and dimensions of the insulator were similar to Example 3except that the wall thickness of the cone shaped insulator was about8.2 mm, and the inside dimensions of the insulator were about the sameas the outer surface of the inner end cone housing in the end coneregion of the pollution control device. The freestanding insulator waspliable and resilient. The bulk shrinkage was about 4.5%, and thecompressibility test results are shown in Table 3.

TABLE 2 Compression Force at Various Mount Densities for Example 4 15Sec Basis Wt Mount Density Gap Peak Force Force (g/m²) (g/ml) (cm)(kN/m²) (kN/m²) Sample 1 1599 0.3 0.533 181 88 Sample 2 1599 0.4 0.399358 178 Sample 3 1599 0.5 0.320 638 315

Example 5

A slurry containing 96.2 weight percent water, 2.97 weight percent heattreated ceramic fibers (described in Example 1), 0.24 weight percentsodium aluminate, 0.3 weight percent latex (“AIRFLEX 600BP” latex), and0.3 weight percent of a 50% solids aqueous active aluminum sulfate wasprepared in a stainless steel mixing tank with an in-line propellermixer. The slurry contained about 183.61 (48.5 gallons) of well water.The sodium aluminate was added with the mixer stirring at medium to highspeed. The ceramic fibers were slowly added and the mixer speed wasincreased to the maximum level to keep the fibers dispersed and break uplarge fiber clumps. After the fibers were dispersed, the latex was addedand mixed for about 5 minutes. Then the aluminum sulfate solution wasadded slowly, and the slurry was mixed for about 10 minutes until it wasuniform. An insulator was made according to the procedure in Example 2.The freestanding insulator was pliable, resilient, and had a bulkshrinkage of about 4.5%. The insulating material was tested forcompressibility at various mount densities and with various basisweights. The results are shown in Table 3.

TABLE 3 Compression Force at Various Mount Densities for Example 5 15Sec Basis Wt Mount Density Gap Peak Force Force (g/m²) (g/ml) (cm)(kN/m²) (kN/m²) Sample 1 1807 0.2 0.904 22 16 Sample 2 1862 0.4 0.465258 157 Sample 3 1883 0.6 0.315 824 451 Sample 4 1827 0.8 0.229 19301043 Sample 1 1807 0.4 0.452 258 156 Sample 1 1807 0.6 0.302 812 460Sample 1 1807 0.8 0.226 1785 1011

The end cone of Example 5 was further evaluated using the Real ConditionFixture Test, and results are shown in Table 4. Pressure was maintainedin the gap between the two platens for three heating and cooling cycles.

TABLE 4 RCFT Results for Example 5 Temperature (° C.) Pressure (kN/m²)Platen 1 Platen 2 Cycle 1 Cycle 2 Cycle 3 25 25 157.73 92.69 89.39 10025 134.6 90.34 86.99 150 30 130.91 88.74 86.08 200 35 130.01 87.49 85.27250 38 123.65 86.45 83.89 300 40 119.43 85.41 82.94 350 45 114 82.6380.18 400 50 100.02 83.11 81.59 450 60 86.13 80.14 78.89 500 70 83.3582.57 78.45 550 85 74.44 78.45 77.76 600 100 69.56 76.27 75.01 650 12562.63 68.19 69.22 700 150 55.75 62.9 61.64 750 185 50.42 56.99 54.73 800220 41.76 49.34 48.83 850 325 32.73 34.41 33.76 900 430 26.58 24.9224.87 900 480 22.61 21.42 21.25 900 530 23.75 18.11 17.8 900 530 23.719.93 19.12 850 502 27.02 22.19 21.66 800 474 29.92 24.81 23.15 750 44534.62 28.3 27.1 700 416 38.31 30.54 29.58 650 387 41.57 34.54 32.68 600358 45.92 37.75 36.19 550 329 49.36 40.94 38.88 500 300 52.79 44.8741.62 450 275 58.21 48.3 45.91 400 250 60.16 50.64 48.33 350 215 63.7155.2 52.86 300 180 69.84 61.37 58.88 250 155 73.14 64.7 62.76 200 13076.75 69.35 65.74 150 95 81.63 75.47 71.93 100 60 86.21 81.27 78.49 5050 87 82.75 79.95

Example 6

An insulator is prepared according to the procedure in Example 3 exceptthat the fibers used are those available under the trade designation“CER-WOOL HP” from Vesuvius, Buffalo, N.Y. that had been heat treatedfor 3 minutes at 1060° C. The fibers are described by the supplier ashaving a composition of 44 to 49 weight percent Al₂O₃, 50 to 54 weightpercent SiO₂, 0 to 0.2 weight percent Fe₂O₃, 0 to 0.1 weight percentTiO₂, and less than 0.5 weight percent of other materials. The fibershad a bulk shrinkage of 3.2%.

Example 7

An insulator is prepared according to the procedure described in Example3 except that the fibers used were those available under the tradedesignation “SNSC” from Shinnika TC (Tokyo, Japan) that were heattreated. The fibers have a composition of about 54 weight percent silicaand about 46 weight percent alumina. The fibers were heat treated at1060° C. and had a bulk shrinkage of 2.6%.

A 28 weight percent SiO₂ and 78 weight percent Al₂O₃ fiber was obtainedunder the trade designation “MAFTEC MLS”; and

a fiber obtained under the trade designation “SAFFIL” was obtained fromSaffil

TABLE 5 Fiber Shrinkage Ex Fiber Heat treating Time (min) Bulk Shrinkage(%) 8 “KAOWOOL ZR” 3.5 5.2 fiber 9 “CER-WOOL HTA” 3 7.6 fiber 10“KAOWOOL HP” 3 2.6 fiber 11 “MAFTEC MLS III” 0 1.1 fiber 12 “SAFFIL LDM”0 1.3 fiber

We claim:
 1. An end cone insulator comprising (a) ceramic fibers havinga bulk shrinkage no greater than 10 percent using the Thermal MechanicalAnalyzer test, (b) an organic binder, and (c) no greater than 40 weightpercent of an inorganic binder based on a weight of the ceramic fibers,wherein said end cone insulator has a seamless one piece truncatedcone-shape that is self-supporting so as to maintain said truncatedcone-shape without collapsing or deforming when placed on a flatsurface, flexible so that it can be bent and flexed gently withoutbreaking apart or cracking, non-intumescent, and dimensioned with atruncated cone-shape suitable for being disposed between inner and outercone-shaped metal end cone housings in an end cone region of a pollutioncontrol device.
 2. The end cone insulator of claim 1, further comprisinga cone-shaped metal end cone housing of a pollution control deviceattached to an inner surface of the end cone insulator, attached to anouter surface of the end cone insulator, or a combination thereof. 3.The end cone insulator of claim 1, wherein the ceramic fibers compriseAl₂O₃ in an amount of at least 20 weight percent and SiO₂ in an amountof at least 30 weight percent based on the weight of the ceramic fibers.4. The end cone insulator of claim 3, wherein said end cone insulatorhas a thickness with a compressibility value no greater than 750 kN/m²when the mount density is about 0.4 g/ml.
 5. The end cone insulator ofclaim 1, wherein the ceramic fibers have a bulk shrinkage no greaterthan 6 percent.
 6. The end cone insulator of claim 1, wherein theceramic fibers have a bulk shrinkage in the range of 0.5 to 5 percent.7. The end cone insulator of claim 6, wherein said end cone insulatorhas a thickness with a compressibility value no greater than 300 kN/m²when the mount density is about 0.4 g/ml.
 8. A pollution control devicecomprising: a housing comprising an inlet and an outlet, and said inletcomprising an inner cone-shaped metal end cone housing and an outercone-shaped metal end cone housing defining a gap therebetween; apollution control element mounted within said housing; a mounting matdisposed between said housing and said pollution control element; and anend cone insulator, according to claim 1, having a thickness and beingsandwiched within the gap between said inner and outer cone-shaped metalend cone housings, with the thickness of said end cone insulator havinga compressibility value no greater than 750 kN/m², when the mountdensity is about 0.4 g/ml, and being in a compressed state while saidend cone insulator is sandwiched within the gap at room temperature,wherein said end cone insulator has a bulk before and a mount densityafter being sandwiched within the gap, the mount density is greater thanthe bulk density, and the thickness of said end cone insulator can befurther compressed and the mount density increased without the ceramicfibers of said end cone insulator breaking or disintegrating.
 9. Apollution control device comprising a housing and an end cone insulatoraccording to claim 1, said housing having an inlet and an outlet, saidinlet comprising an inner cone-shaped metal end cone housing and anouter cone-shaped metal end cone housing defining a gap therebetween,and said end cone insulator being sandwiched between said inner andouter cone-shaped metal end cone housings.
 10. A pollution controldevice comprising a housing and an end cone insulator according to claim4, said housing having an inlet and an outlet, said inlet comprising aninner cone-shaped metal end cone housing and an outer cone-shaped metalend cone housing defining a gap therebetween, and said end coneinsulator being sandwiched between said inner and outer cone-shapedmetal end cone housings.
 11. A method of making an end cone insulatoraccording to claim 1, said method comprising: preparing an aqueousslurry comprising (a) ceramic fibers having a bulk shrinkage no greaterthan 10 percent using the Thermal Mechanical Analyzer test, (b) anorganic binder, and (c) no greater than 40 weight percent of aninorganic binder based on a weight of the ceramic fibers; vacuum forminga seamless one piece truncated cone-shaped preform from the aqueousslurry on a permeable forming cone-shaped die; drying the preform toproduce an end cone insulator, wherein the end cone insulator has aseamless one piece truncated cone-shape that is being self-supporting soas to maintain the truncated cone-shape without collapsing or deformingwhen placed on a flat surface, flexible so that it can be bent andflexed gently without breaking apart or cracking, non-intumescent, anddimensioned with a truncated cone-shape suitable for being disposedbetween inner and outer cone-shaped metal end cone housings in an endcone region of a pollution control device.
 12. The method of claim 11,wherein said vacuum forming further comprises: inserting the preforminto or onto a cone-shaped shape-retaining device while the preform issupported by the permeable forming cone-shaped die, transferring thepreform to the cone-shaped shape-retaining device, and removing thepermeable forming cone-shaped die.
 13. The method of claim 12, whereinthe shape-retaining device is an inner cone-shaped metal end conehousing or an outer cone-shaped metal end cone housing of an end coneregion of a pollution control device.
 14. The method of claim 13,wherein the end cone insulator is attached to the end cone housing. 15.The method of claim 11, wherein the ceramic fibers are microcrystalline,crystalline, or a combination thereof, and the end cone insulator has athickness with a compressibility value no greater than 750 kN/m² whenthe mount density is about 0.4 g/ml.
 16. The method of claim 11, whereinthe ceramic fibers comprise Al₂O₃ in an amount of at least 20 weightpercent and SiO₂ in an amount of at least 30 weight percent based on theweight of the ceramic fibers.
 17. The method of claim 11, wherein theslurry comprises up to 20 weight percent of the organic binder based onthe weight of the end cone insulator.
 18. A method of making a pollutioncontrol device having an end cone region comprising inner and outercone-shaped metal end cone housings, said method comprising: disposingan end cone insulator between the inner and outer cone-shaped metal endcone housings of the pollution control device, where the end coneinsulator is made according to the method of claim
 11. 19. A pollutioncontrol device comprising: a housing comprising an inlet and an outlet,and said inlet comprising an inner cone-shaped metal end cone housingand an outer cone-shaped metal end cone housing defining a gaptherebetween; a pollution control element mounted within said housing; amounting mat disposed between said housing and said pollution controlelement; and an end cone insulator, according to claim 1, having athickness and being sandwiched within the gap between said inner andouter cone-shaped metal end cone housings, with the thickness of saidend cone insulator having a compressibility value no greater than 300kN/m², when the mount density is about 0.4 g/ml, and being in acompressed state while said end cone insulator is sandwiched within thegap at room temperature, wherein said end cone insulator has a bulkdensity in the range of 0.1 to 0.4 g/ml before being sandwiched withinthe gap and a mount density after being sandwiched within the gap thatis greater than the bulk density, and the thickness of said end coneinsulator can be further compressed and the mount density increasedwithout the ceramic fibers of said end cone insulator breaking ordisintegrating.
 20. An end cone insulator comprising (a) ceramic fibershaving a bulk shrinkage no greater than 10 percent using the ThermalMechanical Analyzer test, and (b) a binder, with no greater than 40weight percent of an inorganic binder based on a weight of the ceramicfibers, wherein said end cone insulator has a seamless one piecetruncated cone-shape that is self-supporting so as to maintain saidtruncated cone-shape without collapsing or deforming when placed on aflat surface, flexible so that it can be bent and flexed gently withoutbreaking apart or cracking, non-intumescent, and dimensioned with atruncated cone-shape suitable for being disposed between inner and outercone-shaped metal end cone housings in an end cone region of a pollutioncontrol device.